In the case of such a machine which is known from U.S. Pat. No. 3,125,039, the kneading belt bears on a contact zone of about 150.degree. C. over its outer periphery on the compartmented drum, with a radially acting force resulting from initial tensioning of the kneading belt such that by reason of the friction between the kneading belt and the compartmented drum, the kneading belt is entrained in a non-slip manner. This applied pressure is generated in that the tension of the kneading belt is adjusted by an adjustable tensioning roller. The tension in the kneading belt is in this case so selected that at the commencement of the kneading process, the kneading belt exerts the necessary pressure on a portion of dough to initiate the kneading process. Towards the end of the kneading process, when the dough portion assumes a spherical shape, the belt is lifted off the compartmented drum by the dough portion. Proper functioning can only be achieved with difficulty, since the friction forces between the compartmented drum and the kneading belt are generally insufficient for trouble-free entrainment. If, for this reason, a jockey roller for the kneading belt is constructed as a belt drive roller, then it is necessary also to have quite a considerable tension in the kneading belt to ensure perfect slip-free driving, which in turn has a very adverse effect on the lifting of the kneading belt from the drum in the kneading zone. Furthermore, in the case of a given compartmented drum, it is only possible for dough portions of substantially the same size to be shaped, as otherwise the portions of dough cannot assume the desired and necessary spherical shape and/or the entraining of the kneading belt by the compartmented drum is affected if too large a portion of the kneading belt is lifted off the compartmented drum.
German Pat. No. 28 50 936 has already disclosed a machine for kneading dough portions into round shapes; it has a similarly constructed kneading drum and a corresponding compartmented drum in which there is in the round-shaping portion of the machine a support which over a part of its length measured in the peripheral direction of the compartmented drum, is disposed at a distance from the periphery of the compartmented drum which increases in the direction of rotation of this latter. This, therefore, provides an exactly defined and widening gap which makes it possible for the dough portions to increase their diameter in accordance with the increasing gap between the kneading drum and the support. This support is constituted by rod-shaped supporting rollers which are disposed on an endlessly revolving driveable chain, an endless kneading belt being loosely laid on these rod-shaped supporting rollers and being driven in the direction of rotation by the dough portions and by the supporting rollers. This prior art machine calls for considerable material cost for the supporting arrangement and in addition considerable cost in terms of adjustability of the widening gap. The development of the dough portions while they are being made to a round shape is not always the same; it is instead dependent firstly upon the type of dough, for example the recipe and the quality of flour, and secondly upon the way the dough is managed, in other words, for example, the fermentation times, dough temperature and the like. A dry dough, for instance, develops more slowly than a more moist dough. Consequently, in the case of a dry dough, the kneading belt will be lifted off the kneading drum later than in the case of a more moist dough. Such fine differences can hardly be taken into consideration with a rigidly adjustable kneading belt regime.